This invention relates to a thermoplastic resin composition which is excellent in rigidity and impact resistance in respect of physical properties, has a short molding cycle and characteristic features in surface quality such as no generation of flow mark or weldline, no surface strain or the like in respect of injection moldability, and to an injection molded article excellent in dimension stability molded therefrom by an injection molding method, particularly an automobile interior trim material.
More particularly, this invention relates to a thermoplastic resin composition which comprises a specific crystalline polypropylene as a main component and is excellent in rigidity and impact resistance in respect of physical properties and has a short molding cycle and excellent surface quality in respect of injection moldability; and to an injection molded article excellent in dimension stability prepared therefrom by an injection molding method, particularly an injection molded article for automobile interior trim.
Crystalline ethylene-propylene copolymer/ethylene-propylene copolymer rubber/talc compositions (referred to hereinafter as the ethylene-propylene copolymer rubber type composition) has been widely used as an automobile interior trim material because they are inexpensive, good in moldability and the like. The ethylene-propylene copolymer rubber type resin composition is usually molded into an automobile interior trim material by an injection molding method. As to the injection moldability thereof, it is required firstly that the molding cycle of the present composition be shortened for increasing the productivity; secondly that the present composition give, by an injection molding, an interior trim molded article which has such excellent surface qualities that neither flow mark nor weldline is generated and no surface strain is caused; and the like.
However, conventional ethylene-propylene copolymer rubber type compositions have such problems that when the fluidity thereof is simply increased, the impact strength which is required for an interior trim material is not satisfied though the surface quality is improved in the injection molding and the filling time is shortened but the plasticizing time becomes long and hence the molding cycle is consequently not shortened.
Under such circumstances, this invention aims at providing a themoplastic resin composition which comprises a crystalline polypropylene as a main component, and which, in respect of physical properties, satisfies the impact strength and rigidity required for an interior trim material and has high flow and good balance between impact strength and rigidity as compared with conventionally used ethylene-propylene copolymer rubber compositions, and in respect of injection moldability, has a short molding cycle and good surface quality, and further providing an injection molded article using the composition, particularly an injection molded article for automobile interior trim.
This invention relates to a thermoplastic resin composition comprising (A) a crystalline polypropylene, (B) an ethylene-butene-1 copolymer rubber, (C) an ethylene-propylene copolymer rubber and (D) a vinyl aromatic compound-containing rubber (at least one of the above (B), (C) and (D) is used), (E) talc and (F) fibrous magnesium oxysulfate and to an injection molded article obtained by molding the above thermoplastic resin composition by an injection molding method.
That is to say, this invention relates to a thermoplastic resin composition which comprises:
(1) 57 to 71% by weight of a crystalline polypropylene (A) selected from the following (i) or (ii):
(i) a crystalline ethylene-propylene copolymer in which the propylene homopolymer portion which is the first segment has a Q value of 3 to 5 which is the weight average molecular weight (Mw)/number average molecular weight (Mn) ratio according to a gel permeation chromatography (GPC) method, an isotactic pentad fraction of not less than 0.98 as calculated by 13C-NMR and an intrinsic viscosity of 0.9 to 1.1 dl/g as measured at 135xc2x0 C. in tetralin; and the ethylene-propylene random copolymer portion which is the second segment has an intrinsic viscosity of 4.5 to 5.5 dl/g as measured at 135xc2x0 C. in tetralin and an ethylene/propylene ratio of 25/75 to 35/65 (weight % ratio), and
(ii) a mixture of the crystalline ethylene-propylene block copolymer of (i) with a crystalline propylene homopolymer having a Q value of 3 to 5 according to the GPC method, an isotactic pentad fraction of not less than 0.98 as calculated by 13C-NMR and an intrinsic viscosity of 0.9 to 1.1 dl/g as measured at 135xc2x0 C. in tetralin;
(2) 14 to 18% by weight of at least one rubber component selected from the group consisting of the following (B), (C) and (D):
0 to 5% by weight of the following ethylene-butene-1 copolymer rubber (B):
an ethylene-butene-1 copolymer rubber having a Q value of not more than 2.7 according to the GPC method, a butene-1 content of 15 to 20% by weight, an intrinsic viscosity of 1.1 to 2.1 dl/g as measured at 70xc2x0 C. in xylene and a Mooney viscosity at 100xc2x0 C. (ML1+4 100xc2x0 C.) of 7 to 90,
0 to 5% by weight of the following ethylene propylene copolymer rubber (C):
an ethylene-propylene copolymer rubber having a Q value of not more than 2.7 according to the GPC method, a propylene content of 20 to 30% by weight, an intrinsic viscosity of 1.8 to 2.2 dl/g as measured at 70xc2x0 C. in xylene and a Mooney viscosity at 100xc2x0 C. (ML1+4 100xc2x0 C.) of 35 to 100, and
10 to 18% by weight of the following vinyl aromatic compound-containing rubber (D):
a vinyl aromatic compound-containing rubber in which a vinyl aromatic compound is bonded to an olefinic copolymer rubber or a conjugated diene rubber, and which has a vinyl aromatic compound content of 1 to 50% by weight and a melt viscosity at 230xc2x0 C. at a shear rate of 10 secxe2x88x921 of not more than 104 as measured by a capillary flow tester, and which is characterized in that in a blend prepared by adding 10% by weight of the vinyl aromatic compound-containing rubber to a crystalline propylene homopolymer having an isotactic pentad.fraction of 0.98 as calculated by 13C-NMR and an intrinsic viscosity of 1.55 dl/g as measured at 135xc2x0 C. in tetralin, the difference (xcex94Tg, Tg shift) in glass transition point (Tg) attributed to the crystalline propylene homopolymer portion before and after the blending is less than 3xc2x0 C.;
(3) 15 to 25% by weight of talc having an average particle size of not more than 4 xcexcm (E); and
(4) 0 to 10% by weight of fibrous magnesium oxysulfate having a fiber diameter of 0.3 to 2 xcexcm and an average fiber length of 5 to 50 xcexcm (F),
and which thermoplastic resin composition satisfies the following equations 1) to 4):
(A)+(B)+(C)+(D)+(E)+(F)=100xe2x80x83xe2x80x831)
0.20xe2x89xa6{[(A)xc3x97(A)xe2x80x2+(B)+(C)+(D)]/100}xe2x89xa60.25xe2x80x83xe2x80x832)
0.1xe2x89xa6{(A)xc3x97(A)xe2x80x2/[(A)xc3x97(A)xe2x80x2+(B)+(C)+(D)]}xe2x80x83xe2x80x833)
15xe2x89xa6[(E)+(F)]xe2x89xa625xe2x80x83xe2x80x834)
wherein (A), (B), (C), (D), (E) and (F) indicate weight % of the respective components and (A)xe2x80x2 indicates the weight fraction of the second segment in the crystalline polypropylene (A), and has a melt flow index (JIS-K-6758, 230xc2x0 C.) of 25 to 35 g/10 minutes and a flexural modulus at 23xc2x0 C. of not less than 20,000 kg/cm2; and to an injection molded article obtained from the thermoplastic resin composition, particularly a molded article for automobile interior trim.
This invention is explained below in detail.
In this invention, the crystalline polypropylene (A) means (i) a crystalline ethylene-propylene copolymer having a crystalline propylene homopolymer portion as the first segment and an ethylene-propylene random copolymer portion as a second segment (referred to as the block copolymer in some cases) or (ii) a mixture of such a crystalline ethylene-propylene copolymer with a crystalline propylene homopolymer.
Here, when the crystalline polypropylene (A) is the crystalline ethylene-propylene copolymer (i) which has a crystalline propylene homopolymer portion as the first segment and an ethylene-propylene random copolymer portion as the second segment, the following physical properties, compositions and the like are required:
That is to say, in the crystalline ethylene-propylene copolymer (i), the Q value of the propylene homopolymer portion which is the first segment is 3 to 5, preferably 3.5 to 4.5 which Q value is the weight average molecular weight (Mw)/number average molecular weight (Mn) ratio representing a molecular weight distribution according to a gel permeation chromatography (GPC) method. When the Q value is less than 3, the fluidity is deteriorated and when the Q value exceeds 5, a preferable result is not obtained in relation between the molding cycle and the surface quality during the injection molding.
Furthermore, the isotactic pentad fraction calculated by 13C-NMR is not less than 0.98, preferably not less than 0.985. When it is less than 0.98, it is difficult to satisfy the objective rigidity, heat resistance and the like.
Moreover, the intrinsic viscosity of the propylene homopolymer portion is 0.9 to 1.1 dl/g as measured at 135xc2x0 C. in tetralin. When it exceeds 1.1 dl/g, the melt flow rate of the composition becomes low and the fluidity is deteriorated, the molding cycle becomes long because the filling time becomes long, and simultaneously a good surface quality is not obtained. When it is less than 0.9 dl/g, the tensile elongation and impact strength are low in respect of physical properties and a good surface quality is obtained in respect of injection moldability but the plasticizing time becomes long and hence the molding cycle becomes long and a preferable result is not obtained.
When the ethylene/propylene ratio of the ethylene-propylene random copolymer portion which is the second segment is 25/75 to 35/65 (weight % ratio) (the ethylene content (C2xe2x80x2)EP is 25 to 35% by weight, the total of ethylene and propylene is taken as 100% by weight, the same applies hereinafter), more preferably 27/75 to 32/78 (weight % ratio) (the ethylene content (C2xe2x80x2)EP is 27 to 32% by weight). When the ethylene content is less than 25% by weight or exceeds 35% by weight, a preferable result is not obtained as to the impact resistance of the composition. Moreover, the intrinsic viscosity [xcex7]EP of the ethylene-propylene random copolymer portion is preferably 4.5 to 5.5 dl/g, more preferably 4.8 to 5.3 dl/g, and when it is less than 4.5 dl/g a flow mark is generated during the injection molding and when it exceeds 5.5 dl/g, a hard spot portion is caused and a preferable result is not obtained in respect of surface quality.
When the crystalline polypropylene (A) is (ii) the mixture of the above crystalline ethylene-propylene copolymer (i) with a crystalline propylene homopolymer, the following physical properties, compositions and the like are required:
That is, similarly to the above crystalline ethylene-propylene copolymer (i), the Q value which is the weight average molecular weight (Mw)/number average molecular weight (Mn) ratio representing a molecule distribution according to the (GPC) method is 3 to 5; the isotactic pentad fraction calculated by 13C-NMR is not less than 0.98. Moreover, the intrinsic viscosity of the 10 propylene homopolymer portion is 0.9 to 1.1 dl/g as measured at 135xc2x0 C. in tetralin.
An explanation is made below of methods for measuring the above various physical properties. The isotactic pentad fraction is a fraction of propylene monomer unit existing at the center of an isotactic chain in the form of a pentad unit, in other words, the chain in which five propylene monomer units are successively meso-bonded, in the crystalline polypropylene molecular chain as measured by the method disclosed in A. Zambelli et al., Macromolecules, 6, 925 (1973), namely by use of 13C-NMR. However, the attribution of the NMR absorption peak is based on Macromolecules, 8, 687 (1975) published thereafter.
Moreover, the weight ratio X of the ethylene-propylene random copolymer portion to the overall block copolymer can be determined by calculation from the following equation by measuring the quantity of heat of crystal fusion of each of the crystalline propylene homopolymer portion and the overall block copolymer:
The ethylene content of the ethylene-propylene random copolymer portion can be determined by calculation from the following equation by measuring the ethylene content (weight %) of the overall block copolymer by an infrared absorption spectrum method:
Furthermore, the intrinsic viscosity [xcex7]EP of the ethylene-propylene random copolymer portion as measured at 135xc2x0 C. in tetralin can be determined by calculation from the following equation by measuring the intrinsic viscosity of each of the crystalline homopolymer portion and the overall block copolymer:
[xcex7]EP=[xcex7]T/Xxe2x88x92(1/Xxe2x88x921)[xcex7]P
[xcex7]P: Intrinsic viscosity (dl/g) of crystalline propylene homopolymer portion
[xcex7]T: intrinsic viscosity (dl/g) of overall block copolymer.
In the case of use in applications in which impact resistance is particularly required, it is preferable to use, as the crystalline polypropylene, the crystalline ethylene-propylene copolymer (i) consisting of the crystalline propylene homopolymer portion which is the first segment polymerized in the first step and the ethylene-propylene random copolymer portion which is the second segment polymerized in the second step.
Said copolymer can be produced by a slurry polymerization method, a gas phase polymerization method or the like. In particular, in the case of use in applications in which high impact resistance is required, it is necessary to increase the amount of the second segment and it is preferably produced by the gas phase polymerization method.
The high impact resistance polypropylene according to the said gas phase polymerization method can be produced by the method illustrated in JP-A-61-287,917.
In the slurry polymerization method, the amount of the second segment is 10 to 30% by weight, and in the gas phase polymerization method, it is suitably produced in the range of from 10 to 70% by weight.
In the gas phase polymerization method, it is further possible to produce a crystalline ethylene-propylene block copolymer having a large amount of the second segment by the method illustrated in JP-A-1-98,604, and said copolymer is suitably used in applications in which super high impact resistance is required.
The ethylene-propylene copolymer (i) used in this invention is obtained by reacting the monomers in two stages in the presence of a solid catalyst system comprising, as the essential components, magnesium, titanium, a halogen and an aluminum compound. However, the catalyst system is preferably a catalyst system consisting of (a) a trivalent titanium compound-containing solid catalyst component (a complex of titanium trichloride with magnesium), (b) an organoaluminum compound and (c) an electron-donating compound.
The method for producing this catalyst system is stated in detail in, for example, JP-A-61-218,606, JP-A-1-319,508 and the like.
That is to say, it is a catalyst system consisting of (a) a trivalent titanium compound-containing solid catalyst component obtained by reducing a titanium compound represented by the general formula Ti(OR1)nX4xe2x88x92n in which R1 represents a hydrocarbon group having 1 to 20 carbon atoms, X represents a halogen atom and n is 0 less than nxe2x89xa64 with an organomagnesium compound in the coexistence of a Si-O bond-containing silicon compound and an ester compound and then treating the solid product thus obtained with an ester compound, an ether compound and titanium tetrachloride; (b) an organoaluminum compound; and (c) an electron-donating compound.
The titanium compound used in the synthesis of the above solid catalyst component (a) is that represented by the above-mentioned general formula; however, R1 is preferably an alkyl group having 2 to 18 carbon atoms or an aryl group having 6 to 18 carbon atoms. The halogen atom represented by X can be exemplified by chlorine, bromine and iodine, among which chlorine is particularly preferable.
The value of n of the titanium compound represented by the above general formula is 0 less than nxe2x89xa64, preferably 2xe2x89xa6nxe2x89xa64, particularly preferably n=4.
The organosilicon compound having a Si-O bond used in the synthesis of the above solid catalyst component (a) includes those represented by the general formulas Si(OR2)mR34xe2x88x92m, R4(R52SiO)pSiR63 and (R72SiO)q in which R2 represents a hydrocarbon group having 1 to 20 carbon atoms; R3, R4, R5, R6 and R7 represent hydrocarbon groups having 1 to 20 carbon atoms or hydrogen atoms; m is 0 less than mxe2x89xa64; p is an integer of 1 to 1,000 and q is an integer of 2 to 1,000.
Specific examples of the organosilicon compound include tetramethoxysilane, dimethyldimethoxysilane, diethoxydiethylsilane, diethoxydiphenylsilane, triethoxyphenylsilane, cyclohexylethyldimethoxysilane, phenyltrimethoxysilane and the like. Among these organosilicon compounds, preferable are alkoxysilane compounds represented by the general formula Si(OR2 )mR34xe2x88x92m, preferably 1xe2x89xa6mxe2x89xa64 and particularly preferable is a tetraalkoxysilane compound corresponding to m=4.
As the organomagnesium compound used in the synthesis of the above solid catalyst component (a), there can be used any type of the organomagnesium compounds having a magnesium-carbon bond. In particular, there are suitably used Grignard compounds represented by the general formula R8MgX in which R8 represents a hydrocarbon group having 1 to 20 carbon atoms and X represents a halogen and dialkylmagnesium compounds or diarylmagnesium compounds represented by the general formula R9R10Mg in which R9 and R10 are hydrocarbon groups having 1 to 20 carbon atoms. Here, R9 and R10 may be the same or different.
As the ester compound used in the synthesis of the above solid catalyst component (a), there are mentioned mono- and polycarboxylic acid esters such as aliphatic carboxylic acid esters, olefinic carboxylic acid esters, alicyclic carboxylic acid esters, aromatic carboxylic acid esters and the like. Among these ester compounds, preferable are olefinic carboxylic acid esters such as methacrylic acid esters, maleic acid esters and the like and phthalic acid esters, and particularly preferable are diesters of phthalic acid.
In addition, as the ether compound, preferable are dialkyl ethers such as diethyl ether, di-n-propyl ether, diisopropyl ether, dibutyl ether, diamyl ether, methyl-n-butyl ether and the like, and particularly preferable are di-n-butyl ether and diisoamyl ether.
The above solid catalyst component (a) is synthesized by reducing a titanium compound with a magnesium compound in the presence of an organosilicon compound and an ester compound, treating the resulting solid product with an ester compound, and thereafter treating the product with a mixture of an ether compound and titanium tetrachloride or a mixture of an ether compound, titanium tetrachloride and an-ester compound. These synthesis reactions are all effected in an atmosphere of an inert gas such as nitrogen, argon or the like.
The reduction reaction temperature is in a temperature range from xe2x88x9250xc2x0 C. to 70xc2x0 C., preferably from xe2x88x9230xc2x0 C. to 50xc2x0 C., and particularly preferably from xe2x88x9225xc2x0 C. to 35xc2x0 C.
The organoaluminum compound of the above component (b) is one having at least one aluminum-carbon bond in the molecule and represented by the general formula R11rAlY3xe2x88x92r or R12R13Alxe2x80x94Oxe2x80x94AlR14R15 in which R11 to R15 represent hydrocarbon groups having 1 to 20 carbon atoms, Y represents a halogen, hydrogen or an alkoxy group and r is 2xe2x89xa6rxe2x89xa63.
Specific examples of the organoaluminum compound include trialkylaluminums such as triethylaluminum, triisobutylaluminum, trihexylaluminum and the like; dialkylaluminum halides such as diethylaluminum halides, diisobutylaluminum halides and the like; mixtures of triethylaluminum and dialkylaluminum halides; and alkylalumoxanes such as tetraethyldialumoxane, tetrabutyldialumoxane and the like.
Among these organoaluminum compounds, preferable are trialkylaluminums, mixtures of trialkylaluminums with diethylaluminum chloride, and tetraethyldialumoxane.
The amount of the organoaluminum compound used can usually be selected from such a broad range as 0.5 to 1,000 moles per mole of titanium atom in the solid catalyst component (a); however, the range of from 1 to 600 moles is preferable.
As the electron-donating compound of the above component (c), there can be mentioned oxygen-containing electron donors such as alcohols, phenols, ketones, aldehydes, carboxylic acids, esters of organic acids or inorganic acids, ethers, acid amides, acid anhydrides and the like; nitrogen-containing electron donors such as ammonias, nitrites, isocyanates and the like; etc. Among these electron donors, esters of inorganic acids and ethers are preferably used.
The ratio of the aluminum compound of the component (b) and the complex of titanium compound with magnesium compound of the component (a) can be selected from the range of from 3/1 to 20/1 by mole. Moreover, the ratio between the silane compound having a Sixe2x80x94O bond and the complex of the titanium compound with the magnesium compound can be selected from the range of from 1/10 to 1/2 by mole.
The ethylene-butene-1 copolymer rubber (B) in this invention means a random copolymer rubber of ethylene and butene-1 and is commercially available. The butene-1 content of the ethylene-butene-1 copolymer rubber is 15 to 20% by weight, preferably 16 to 19% by weight, and more preferably 17 to 18% by weight. When it is less than 15% by weight, a preferable result is not obtained as to impact resistance, and when it exceeds 20% by weight, a preferable result is not obtained as to rigidity.
The Q value of the ethylene-butene-1 copolymer rubber according to the GPC method is not more than 2.7, preferably not more than 2.5. The intrinsic viscosity is 1.1 to 2.1 dl/g as measured at 70xc2x0 C. in xylene and the Mooney viscosity at 100xc2x0 C. (ML1+4 100xc2x0 C.) is 7 to 90, and these are preferably 1.2 to 2.0 dl/g and 10 to 80, respectively. When the Q value exceeds 2.7, the rigidity becomes low and this is not desirable. When the intrinsic viscosity is less than 1.1 dl/g as measured at 70xc2x0 C. in xylene and the Mooney viscosity at 100xc2x0 C. (ML1+4 100xc2x0 C.) is less than 7, preferable results are not obtained as to rigidity and impact strength, and when these exceed 2.0 dl/g and 90, respectively, the dispersion thereof in the crystalline polypropylene (A) becomes bad and a preferable result is not obtained as to impact strength.
The ethylene-propylene copolymer rubber (C) in this invention means a random copolymer rubber of ethylene and propylene or an ethylene-propylene-non-conjugated diene copolymer rubber, and is commercially available. The propylene content of the ethylene-propylene copolymer rubber is 20 to 30% by weight, preferably 22 to 28% by weight. When it is less than 20% by weight, a preferable result is not obtained as to impact strength, and when it exceeds 30% by weight, a preferable result is not obtained as to rigidity. It is preferable to control the non-conjugated diene content of the copolymer rubber to not more than 7% by weight. When the non-conjugated diene content exceeds 7% by weight, gelation is caused during the kneading and hence it is not desirable.
The Q value according to the GPC method of the ethylene-propylene copolymer rubber is not more than 2.7, preferably not more than 2.5. The intrinsic viscosity is 1.8 to 2.2 dl/g as measured at 70xc2x0 C. in xylene and the Mooney viscosity at 100xc2x0 C. (ML1+4 100xc2x0 C.) is 35 to 100, and these are preferably 1.9 to 2.1 dl/g and 50 to 90, respectively.
When the Q value exceeds 2.7, the rigidity becomes low and this is not desirable. When the intrinsic viscosity is less than 1.8 dl/g as measured at 70xc2x0 C. in xylene and the Mooney viscosity at 100xc2x0 C. (ML1+4 100xc2x0 C.) is less than 35, preferable results are not obtained as to rigidity and impact strength. When these exceed 2.2 dl/g and 100, respectively, the dispersion thereof in the crystalline polypropylene (A) becomes bad and a preferable result is not obtained with respect to impact strength.
The vinyl aromatic compound-containing rubber (D) in this invention includes rubbers in which a vinyl aromatic compound is bonded to an olefinic copolymer rubber or a conjugated diene rubber by polymerization, reaction or the like, for example, block and random copolymers such as styrene-butadiene type rubber (SBR), styrene-butadiene-styrene type rubber (SBS), styrene-isoprene-styrene type rubber (SIS) and the like; these block and random copolymer rubbers in which the rubber components have been hydrogenated; and the like. It is also possible to suitably use a rubber in which a vinyl aromatic compound such as styrene or the like has been reacted with an ethylene-propylene-non-conjugated diene type rubber (EPDM).
The vinyl aromatic compound-containing rubber has a vinyl aromatic compound content of 1 to 50% by weight, preferably 5 to 40% by weight, and more preferably 10 to 30% by weight and a melt viscosity at 230xc2x0 C. at a shear rate of 10 secxe2x88x921 of not more than 10xe2x88x924 as measured by a capillary flow tester; and is a vinyl aromatic compound-containing rubber characterized in that in a blend of 10% by weight of the vinyl aromatic compound-containing rubber with a crystalline propylene homopolymer having an isotactic pentad fraction of 0.98 as measured by 13C-NMR and an intrinsic viscosity of 1.55 dl/g as measured at 135xc2x0 C. in tetralin, the difference (xcex94Tg, Tg shift) in glass transition point (Tg) attributed to the crystalline propylene homopolymer portion before and after the blending is less than 3xc2x0 C.
When the Tg shift is not less than 3xc2x0 C., it becomes compatible with the polypropylene homopolymer portion in the composition to reduce the rigidity and when the melt viscosity is higher than 104 the fluidity of the composition is deteriorated and, in addition, dispersion failure is caused and even impact strength is reduced.
In this invention, in the final composition, at least one member of the ethylene-butene-1 copolymer rubber (B), the ethylene-propylene copolymer rubber (C) and the vinyl aromatic compound-containing rubber (D) is necessary to use.
The total content of the above (B) to (D) in the final composition is 14 to 18% by weight. Moreover, when the amount of the second segment of the crystalline ethylene-propylene block copolymer of (A) is included, [(A)xc3x97(A)xe2x80x2+(B) to (D)] is necessary to satisfy the following equations:
(A)+(B)+(C)+(D)+(E)+(F)=100xe2x80x83xe2x80x831)
0.20xe2x89xa6{[(A)xc3x97(A)xe2x80x2+(B)+(C)+(D)]/100}xe2x89xa60.25xe2x80x83xe2x80x832)
0.1xe2x89xa6{(A)xc3x97(A)xe2x80x2/[(A)xc3x97(A)xe2x80x2+(B)+(C)+(D)]}xe2x80x83xe2x80x833)
When the values are less than these lower limits, a preferable result is not obtained in respect of impact strength, and when the values exceed the above upper limits the fluidity of the composition is deteriorated.
The average particle diameter of the talc (E) used in this invention is not more than 4 xcexcm, preferably not more than 3 xcexcm. When it is more than 4 xcexcm, the reduction of impact strength is large, and an appearance such as gloss or the like becomes bad. The talc may be used without being treated; however, it is possible to use talc whose surface has been treated with various usually known silane coupling agents, titanium-coupling agents, higher fatty acids, higher fatty acid esters, higher fatty acid amides, higher fatty acid salts or other surfactants for the purpose of enhancing the interfacial adhesiveness to the polypropylene type resin and enhancing the dispersibility.
Here, the average particle diameter of talc means a fifty percent particle diameter D50 determined from an integral distribution curve of the undersize method obtained by subjecting a suspension of the particles in a dispersion medium such as water, alcohol or the like to measurement using a centrifugal settling type particle size distribution measuring apparatus.
The fibrous magnesium oxysulfate (F) used in this invention has an average fiber length of 5 to 50 xcexcm, preferably 10 to 30 xcexcm and an average fiber diameter of 0.5 to 1.0 xcexcm.
As specific physical properties of the final composition, it is necessary that the melt flow index (JIS-K-6758, 230xc2x0 C., a load of 2.16 kg) be 25 to 35 g/10 minutes and the rigidity be such that the flexural modulus at 23xc2x0 C. is not less than 20,000 kg/cm2.
Moreover, it is desirable that the impact strength is such that the Izod impact strength (notched) at 23xc2x0 C. is not less than 25 kg.cm/cm and the brittle temperature is not more than 0xc2x0 C.
The proportions of the above components (E) and (F) contained are required to satisfy the equation 4) 15xe2x89xa6[(E)+(F)]xe2x89xa625. When the proportions are outside these ranges, the thermoplastic resin composition is inferior in heat resistance and when the proportions exceed the upper limits the composition becomes inferior in fluidity and appearance of a molded article, which are not desirable.
The thermoplastic resin composition aimed at by this invention can be obtained only when the structure of each of the components used is specified as mentioned above and the proportion of each of the components blended is limited to the specific range.
The composition of this invention can be produced using a kneader such as a single screw extruder, a twin screw extruder, a Banbury mixer, a hot roll or the like. The mixing of each component may be effected at the same time or may be effected in portions. As a method of adding them in portions, there are a method in which the crystalline polypropylene is kneaded with the talc and thereafter the ethylene-butene-l copolymer rubber, the ethylene-propylene copolymer rubber and the vinyl aromatic compound-containing rubber (these are referred to hereinafter as the rubber collectively) are added and a method in which the crystalline polypropylene is previously kneaded with the talc at a high concentration to form a master batch and this is separately kneaded while it is diluted with the crystalline polypropylene, the rubber or the like. In addition, as a second method of adding them in portions, there are a method in which the crystalline polypropylene is kneaded with the rubber and thereafter the talc is added to and kneaded with them and a method in which the crystalline polypropylene is kneaded with the rubber at a high concentration to form a master batch and thereafter the crystalline polypropylene and the talc are added to and kneaded with the same. As a third method of adding them in portions, there is a method in which the crystalline polypropylene is previously kneaded separately with each of the talc and the rubber and the resulting mixtures are finally kneaded together. The temperature and time required for the kneading are 170 to 250xc2x0 C. and 1 to 20 minutes, respectively.
Moreover, in these kneaders, in addition to these basic components, there can be compounded an additive such as an antioxidant, an ultraviolet absorber, a lubricant, a pigment, an antistatic agent, a copper-pollution-preventing agent, a flame retardant, a neutralizing agent, a foaming agent, a plasticizer, a nucleating agent, a foam inhibitor, a cross-linking agent or the like.
Incidentally, the thermoplastic resin composition of this invention can be formed into an injection molded article by an injection molding method adopted generally. In particular, it is suitably used as an injection molded article for automobile such as door trim, pillar, instrumental panel or the like.